Field of the Invention
The present invention relates to a printing apparatus in which a sheet handling device is connected to a subsequent stage of an image forming device typified by a printer, a copier, and the like.
An image forming device has been practically used in which a sheet handling device typified by, for example, a finisher comprising a post processing apparatus such as a stacker having a sheet tray or a stapler is connected to a subsequent stage of an image forming device typified by a printer, a copier, and the like, thereby improving the handleability of printed sheets, the working efficiency, etc.
The sheet handling device has a post processing function such as a stapler or a sheet folding blade. Sheets transported from the image forming device are further transported to and aligned in a stacking tray having a function of stacking and aligning sheets. When the number of stacked sheets reaches a prescribed number, the bundle of the sheets is stitched at a middle position. The stitched bundle of sheets is transported to a folding machine which folds a bundle of sheets in two. The folding machine folds the bundle of sheets in two by using the stitched position as a reference, to produce a booklet.
Hereinafter, the process of stitching a middle position of a bundle of sheets and folding in two the bundle of sheets at the stitched position is referred to as xe2x80x9csaddle-stitching and folding processxe2x80x9d.
Alternatively, another post processing apparatus may be connected to the subsequent stage of the sheet handling device, so that a sheet transported from the image forming device is passed through the above-mentioned stacking tray and then discharged to the post processing apparatus connected to the subsequent stage of the sheet handling device.
In the sheet handling device, also a sheet feeding apparatus (inserter) may be mounted. In this case, the sheet handling device has a mechanism in which a sheet fed from the inserter enters a sheet transporting path in front of the stacking tray, so that the sheet fed from the inserter can be inserted into sheets transported from the image forming device.
In the case where the saddle-stitching and folding process is to be conducted by using such an inserter, when a sheet is fed from the inserter at a timing when the sheet is transported to the stacking tray in advance of sheets transported from the image forming device, the bundle of sheets which has undergone the saddle-stitching and folding process is formed as a booklet in which the sheet fed from the inserter is used as a cover.
In the case where sheets are to be discharged by using the inserter to the post processing apparatus connected to the subsequent stage of the sheet handling device, when colored sheets (in this case, the color is different from that of sheets transported from the image forming device) are housed in the inserter and the sheets of the inserter are inserted into those which are transported from the image forming device and being transported in the sheet handling device, the sheets which are discharged to and stacked in the post processing apparatus are partitioned by the colored sheets fed from the inserter. Hereinafter, the process of inserting a sheet(s) into sheets to partition the sheets is referred to as xe2x80x9csheet inserting processxe2x80x9d.
In a system in which an image forming device is connected to such a sheet handling device, when the saddle-stitching and folding process is to be conducted by using an inserter, the image forming device starts the operation of feeding sheets from a sheet housing section, in consideration of the time period required for a sheet fed from the inserter to be discharged to a stacking tray. In this case, the saddle-stitching and folding process or the sheet inserting process is conducted while the interval between the sheet fed from the inserter and sheets fed from the image forming device is set to be as small as possible, thereby improving the productivity. In the case where the saddle-stitching and folding process or the sheet inserting process is conducted by using an inserter, therefore, it is usual that sheets are first transported from the image forming device and a sheet is then transported from the inserter.
The image forming device transports sheets before a sheet fed from the inserter is discharged to the stacking tray or the post processing apparatus in the subsequent stage of the sheet handling device. At the timing when the last sheet of the inserter is fed and it is detected that there is no sheet in the inserter, therefore, a plurality of sheets already exist in the image forming device. In the case where the saddle-stitching and folding process or the sheet inserting process is to be conducted, therefore, the several sheets fail to contain a sheet from the inserter which is to be subjected together with the sheets to the process. As a result, the saddle-stitching and folding process or the sheet inserting process cannot be conducted, and the sheets remain in the image forming device, thereby causing a problem in that the remaining sheets must be removed away.
The present invention has been made to solve the above problem with the conventional art.
The problem can be solved by a configuration wherein, in a state where the number of sheets in an inserter of an sheet handling device is detected to be smaller than a predetermined number by using a sheet residual amount detecting sensor for detecting that the number of sheets in the inserter is smaller than a certain reference number, a timing of transporting a sheet from an image forming device is changed in accordance with the state of the sheet residual amount detecting sensor so that, after a sheet fed from the inserter is discharged to a stacking tray or a post processing apparatus in a subsequent stage of the sheet handling device, a sheet is transported from the image forming device.